[cryptography] open letter to Phil Zimmermann and Jon Callas of Silent Circle, re: Silent Mail shutdown
zooko at leastauthority.com
Fri Aug 16 17:46:10 EDT 2013
also posted here: https://leastauthority.com/blog/open_letter_silent_circle.html
This open letter is in response to the `recent shutdown of Lavabit`_ ,
the ensuing `shutdown of Silent Circle's “Silent Mail” product`_, `Jon
Callas's posts about the topic on G+`_, and `Phil Zimmermann's
interview in Forbes`_. Also, of course, all of this is unfolding in
the context of the `2013 Mass Surveillance Scandal`_.
Dear Phil and Jon: Hello there! It is good to have a chance to chat
with you in public.
Please accept the following in the spirit of constructive criticism in
which it is intended.
For those readers who don't know, I've known you both, personally and
professionally for decades. You've each written texts that I've
learned from, inspired me to follow your example, we've worked
together successfully, and you've mentored me. I have great respect
for your technical abilities, your integrity, and your general
reasonableness. Thank you for the all of that and for holding fast to
your principles today, when we need it more than ever.
Your job is not yet done. Your customers are currently vulnerable to
having all of their communications secretly monitored.
I just subscribed to the service at https://SilentCircle.com, and
after I paid $120 for one year of service, it directed me to install
the Silent Text app from Silent Circle on my android phone, which I
did. Now, when I use that Silent Circle app to send text messages to
other Silent Circle customers, I have no way of verifying whether it
is really encrypting my message on my own phone, and if it is really
keeping the encryption key only for me, or if it is leaking the
contents of my messages or my encryption keys to you or to others.
If some attacker, for example the U.S. Federal Government — or to pick
a different example the Zetas Mexican drug cartel — were to coerce
Silent Circle into cooperating with them, then that attacker would
simply require Silent Circle to distribute an update to the app,
containing a backdoor.
There is no way for me to verify that any given version of Silent
Text, including the one that I just installed, is correctly generating
strong encryption keys and is protecting those keys instead of leaking
Therefore, how are your current products any safer for your users that
the canceled Silent Mail product was? The only attacker against whom
your canceled Silent Mail product was vulnerable but against whom your
current products are safe is an attacker who would require you to
backdoor your server software but who wouldn't require you to backdoor
your client software.
Does that constraint apply to the U.S. Federal Government entities who
are responsible for PRISM, for the shut-down of Lavabit, and so much
else? No, that constraint does not apply to them. This was
demonstrated in the Hushmail case in which the U.S. DEA asked Hushmail
(a Canadian company) to turn over the plaintext of the email of one of
its customers. Hushmail complied, shipping a set of CDs to the DEA
containing the customer's messages.
The President of Hushmail `emphasized`_ in interviews with journalists
at the time that Hushmail would be able to comply with such orders
regardless of whether the customer used Hushmail's “client-to-server”
(SSL) encryption or its “end-to-end” (Java applet) encryption.
.. _emphasized: http://www.wired.com/threatlevel/2007/11/hushmail-to-war/
Phil had been Chief Cryptographer of Hushmail years earlier, and was
still a member of the Advisory Board of Hushmail at the time of that
case. He commented about the case at that time, and he also `stated`_,
correctly, that the Hushmail model of *unverified* end-to-end
encryption was vulnerable to government coercion. That's the same
model that Silent Circle uses today.
.. _stated: http://www.wired.com/threatlevel/2007/11/pgp-creator-def/
You have just taken the courageous act of publicly shutting down the
Silent Mail product, and publicly stating your reasons for doing so.
This, then, is your opportunity to make your stance consistent by
informing your customers of the similar dangers posed by the software
distribution practices currently used by Silent Circle (along with
most of the rest of the industry).
I don't know the perfect solution to the problem of the
*unverifiability* of today's software. But being frank about the
current approach and the vulnerability that it imposes on users is the
first step. People will listen to you about this, now. Let's start
talking about it and we can start finding solutions.
Also, warn your users. Don't tell them the untruth that it is
impossible for you to eavesdrop on their communications even if you
try (as your company seems to be on the borderline of doing in public
statements like these: [ `¹`_, `²`_]).
.. _¹: http://www.forbes.com/sites/parmyolson/2013/07/15/corporate-customers-flock-to-anti-snooping-app-silent-circle/
.. _²: http://techcrunch.com/2013/08/08/silent-circle-preemptively-shuts-down-encrypted-email-service-to-prevent-nsa-spying/
We're trying an approach to this problem, here at LeastAuthority.com,
of “*verifiable* end-to-end security”. For our data backup and storage
service, all of the software is Free and Open Source, and it is
distributed through channels which are out of our direct control, such
as Debian and Ubuntu. Of course this approach is not perfectly secure
— it doesn't guarantee that a state-level actor cannot backdoor our
customers. But it does guarantee that *we* cannot backdoor our
This currently imposes inconvenience on our customers, and I'm not
saying it is the perfect solution, but it shows that there is more
than one way to go at this problem.
Thank you for your attention to these important matter, and your
leadership in speaking out about them.
(By the way, LeastAuthority.com is not a competitor to Silent Circle.
We don't offer voice, text, video, or email services, like Silent
Circle does/did. What we offer is simply secure offsite *backup*, and
a secure cloud storage API that people use to build other services.)
.. _recent shutdown of Lavabit:
.. _shutdown of Silent Circle's “Silent Mail” product:
.. _Jon Callas's posts about the topic on G+:
.. _Phil Zimmermann's interview in Forbes:
.. _2013 Mass Surveillance Scandal:
More information about the cryptography